Three aspects of circulation regulation by vascular receptors are discussed, with particular attention to involvement of presso- and chemoceptive reflexes in the circulatory homeostasis of the normal intact animal. Firstly, it is demonstrated that in the acute decorticate cat presso- and chemoceptive stimuli can influence the hypothalamic centers responsible for sham rage behavior. Therefore, besides the medullary cardiovascular and respiratory centers, other neural mechanisms, endowed with more integrative functions and controlling behavioral patterns, are also within the sphere of influence of sino-aortic reflexes. Secondly, other experiments have been reported to show how far the activity of central neural mechanisms may influence visceral, and particularly circulatory, reflex responses. By means of graded electrical stimulation of an aortic nerve in decorticate cats, subsequently decerebrated, it has been concluded that the central excitatory state of the decerebrate preparation favors the inhibitory (i. e. pressoceptive) afferent inflow, while the central excitability of the decorticate animal favors the excitatory (i. e. chemoceptive) inflow. Finally, recent experiments on blood pressure changes during deep sleep have provided greater insight on the role played by sino-aortic reflexes in the normal free-moving animal. In cats with intacts sino-aortic reflexes, episodes of deep sleep are accompanied by marked falls in both systolic and diastolic blood pressure. Much larger falls are however observed in animals after bilateral sino-aortic deafferentation: such low pressure values can be attained in these animals during deep sleep, that episodes of transient cerebral ischemia (electroencephalographic flattening and seizures) are sometimes observed.
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